Systems for protein-protein interaction screening

ABSTRACT

Described herein are methods and systems useful for interrogating protein-protein interactions. These systems utilize non-functional fragments of polypeptides that can complement each other to form a fully functional fragment in vivo. The fully functional polypeptide releases a transcription regulating polypeptide that can bind and activate or repress a reporter element.

CROSS REFERENCE

This application claims the benefit of U.S. Provisional Application No. 62/776,992 filed Dec. 7, 2018, which application is incorporated herein by reference.

SUMMARY

Described herein are nucleic acids, systems, and methods useful for interrogating protein-protein interactions, screening for antagonists or agonists of protein-protein interactions or discovering novel protein-protein interactions. These nucleic acids and systems are useful for screening small-molecule or biologic agonists or antagonists of signaling pathways, such as G-protein coupled receptors, receptor tyrosine kinases, ion channels, and nuclear receptors. In one aspect, the system comprises nucleic acids that encode: a) a bait protein fused to a non-functional fragment of an enzyme that can cleave a target sequence, or that can be cleaved by an endogenous enzyme; b) a prey protein (e.g., a test protein) fused to a non-functional fragment of an enzyme that can cleave a target sequence, or that can be cleaved by an endogenous enzyme that complements the enzyme or target sequence in a), and a transcription regulating protein; and c) a reporter gene under the control of a regulatory element that can be bound by the transcription regulating protein. Association of the bait and prey reconstitutes a fully functional enzyme or target sequence that allows the transcription regulating protein to be cleaved and to activate the reporter gene. In this system the reporter gene comprises a unique molecular identifier (UMI), which is unique to each individual prey protein. This allows for multiplexing of an assay that can interrogate the effect any given stimulus has on bait and prey interaction.

In one aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide coupled to a first fragment of a ubiquitin polypeptide; (b) a second nucleic acid encoding a prey polypeptide coupled to a second fragment of a ubiquitin polypeptide and a transcription regulating polypeptide; and (c) a third nucleic acid comprising a reporter element, wherein said reporter element comprises a regulatory element, a first reporter gene and a second reporter gene, wherein said regulatory element is configured to be bound by said transcription regulating polypeptide, wherein said second reporter gene encodes an RNA sequence that is unique to said prey polypeptide; wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, and initiates transcription of said first reporter gene and said second reporter gene. In certain embodiments, said first fragment of a ubiquitin polypeptide is a C-terminal fragment of a ubiquitin polypeptide, and said second fragment of a ubiquitin polypeptide is an N-terminal fragment of a ubiquitin polypeptide. In certain embodiments, said first fragment of a ubiquitin polypeptide is an N-terminal fragment of a ubiquitin polypeptide, and said second fragment of a ubiquitin polypeptide is a C-terminal fragment of a ubiquitin polypeptide. In certain embodiments, said transcription regulating polypeptide comprises a synthetic transcription factor. In certain embodiments, said synthetic transcription factor comprises a fusion of a Gal4 DNA binding domain and-VPR activation domain. In certain embodiments, said bait polypeptide or said prey polypeptide is a membrane bound signaling polypeptide. In certain embodiments, said membrane-bound bait polypeptide or said prey polypeptide comprises a G protein coupled receptor, a receptor tyrosine kinase, or an ion channel. In certain embodiments, said membrane-bound bait polypeptide or said prey polypeptide comprises a G protein coupled receptor. In certain embodiments, said bait polypeptide or said prey polypeptide is an intracellular signaling polypeptide. In certain embodiments, said intracellular bait polypeptide or said prey polypeptide comprises a nuclear hormone receptor. In certain embodiments, said bait polypeptide or said prey polypeptide comprises an intracellular molecule that potentially interacts with said signaling polypeptide. In certain embodiments, said regulatory element comprises an inducible regulatory element. In certain embodiments, said inducible regulatory element comprises a Gal4 Upstream activation Sequence (Gal4 UAS). In certain embodiments, said first reporter gene encodes a fluorescent protein, a luciferase protein, a beta-galactosidase, a beta-glucuronidase, a chloramphenicol acetyltransferase, or a secreted placental alkaline phosphatase. In certain embodiments, said first reporter gene encodes a fluorescent protein or a luciferase protein. In certain embodiments, said first nucleic acid comprises a sequence encoding a promoter-less fluorescent protein. In certain embodiments, said fluorescent protein is a green fluorescent protein. In certain embodiments, said first nucleic acid comprises a sequence that directs site specific integration into a genome. In certain embodiments, said first nucleic acid comprises an attB sequence that directs site specific integration into a genome. In certain embodiments, said second nucleic acid comprises a sequence encoding a selectable surface marker. In certain embodiments, said selectable surface marker is a hemagglutinin polypeptide. In certain embodiments, described herein, is a cell comprising said first nucleic acid, said second nucleic acid, and/or said third nucleic acid. In certain embodiments, said first nucleic acid, said second nucleic acid, and/or said third nucleic acid are integrated at an integration site for a transposable element. In certain embodiments, said first nucleic acid, said second nucleic acid, and/or said third nucleic acid are integrated at a predetermined genomic location. In certain embodiments, described herein, is a method for testing a test substances effect on a protein-protein interaction comprising contacting a cell or a populations of cells comprising the system described herein to said test substance. In certain embodiments, the test substance is a chemical.

In one aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide; (b) a second nucleic acid encoding a prey polypeptide coupled to a second fragment of a protease polypeptide; and (c) a third nucleic acid comprising a reporter element, wherein said reporter element comprises a regulatory element, a first reporter gene and a second reporter gene, wherein said regulatory element is configured to be bound by said transcription regulating polypeptide, wherein said second reporter gene encodes an RNA sequence that is unique to said prey polypeptide; wherein said first fragment of a protease polypeptide and said second fragment of a protease polypeptide form an active protease when said bait polypeptide interacts with said prey polypeptide, whereupon said protease cleavage site is cleaved by said active protease, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said first reporter gene and said second reporter gene. In certain embodiments, said first fragment of a protease polypeptide is a C-terminal fragment of a protease polypeptide, and said second fragment of a protease polypeptide is an N-terminal fragment of a protease polypeptide. In certain embodiments, said first fragment of a protease polypeptide is a N-terminal fragment of a protease polypeptide, and said second fragment of a protease polypeptide is a C-terminal fragment of a protease polypeptide. In certain embodiments, said first fragment of a protease polypeptide and said second fragment of a protease polypeptide are derived from Tobacco Etch Virus nuclear-inclusion-a endopeptidase (TEV protease). In certain embodiments, said transcription regulating polypeptide comprises a synthetic transcription factor. In certain embodiments, said synthetic transcription factor comprises a fusion of a Gal4 DNA binding domain and-VPR activation domain. In certain embodiments, said second nucleic acid encodes a second transcription regulating polypeptide coupled to said prey polypeptide, wherein said second transcription regulating polypeptide is configured to be cleaved by said active protease. In certain embodiments, said bait polypeptide or said prey polypeptide is a membrane bound signaling polypeptide. In certain embodiments, said membrane-bound bait polypeptide or said prey polypeptide comprises a G protein coupled receptor, a receptor tyrosine kinase, or an ion channel. In certain embodiments, said membrane-bound signaling polypeptide or said prey polypeptide comprises a G protein coupled receptor. In certain embodiments, said bait polypeptide or said prey polypeptide is an intracellular signaling polypeptide. In certain embodiments, said intracellular bait polypeptide or said prey polypeptide comprises a nuclear hormone receptor. In certain embodiments, said bait polypeptide or said prey polypeptide comprises an intracellular molecule that potentially interacts with said bait polypeptide. In certain embodiments, said regulatory element comprises an inducible regulatory element. In certain embodiments, said inducible regulatory element comprises a Gal4 Upstream activation Sequence (Gal4 UAS). In certain embodiments, said first reporter gene encodes a fluorescent protein, a luciferase protein, a beta-galactosidase, a beta-glucuronidase, a chloramphenicol acetyltransferase, a secreted placental alkaline phosphatase. In certain embodiments, said first reporter gene encodes a fluorescent protein or a luciferase protein. In certain embodiments, said first nucleic acid comprises a sequence encoding a promoter-less fluorescent protein. In certain embodiments, said fluorescent protein is a green fluorescent protein. In certain embodiments, said first nucleic acid comprises a sequence that directs site specific integration into a genome. In certain embodiments, said first nucleic acid comprises an attB sequence that directs site specific integration into a genome. In certain embodiments, said second nucleic acid comprises a sequence encoding a selectable surface marker. In certain embodiments, said selectable surface marker is a hemagglutinin polypeptide. In certain embodiments, described herein, is a cell comprising said first nucleic acid, said second nucleic acid, and/or said third nucleic acid. In certain embodiments, said first nucleic acid, said second nucleic acid, and/or said third nucleic acid are integrated at an integration site for a transposable element. In certain embodiments, said first nucleic acid, said second nucleic acid, and/or said third nucleic acid are integrated at a predetermined genomic location. In certain embodiments, described herein, is a method for testing a test substances effect on a protein-protein interaction comprising contacting a cell or a populations of cells comprising the system described herein to said test substance. In certain embodiments, the test substance is a chemical.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts a schematic of a split protease (left) or split-ubiquitin (right) protein-protein interaction system at steady state before binding of bait polypeptide (ARRB2) to a prey polypeptide (membrane-associated).

FIG. 1B depicts a schematic of a split protease (left) or split-ubiquitin (right) protein-protein interaction system at steady state after binding of bait polypeptide (ARRB2) to a prey polypeptide (membrane-associated).

FIG. 2 illustrates fold induction of a luminescent reporter split-ubiquitin compared to a dual-split-TEV system.

FIG. 3A depicts a dose response curve of cells using a split-ubiquitin protein-protein interaction system and treated with Xamoterol.

FIG. 3B depicts a dose response curve of cells using a dual-split-TEV protein-protein interaction system and treated with Xamoterol.

DETAILED DESCRIPTION

In one aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a ubiquitin polypeptide; (b) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a ubiquitin polypeptide, and a transcription regulating polypeptide; and (c) a third nucleic acid comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element.

In another aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a ubiquitin polypeptide; and (b) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a ubiquitin polypeptide, and a transcription regulating polypeptide and comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element.

In another aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a ubiquitin polypeptide, and comprising a regulatory element, which is bound by a transcription regulating polypeptide and a reporter element; and (b) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a ubiquitin polypeptide, and said transcription regulating polypeptide; wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element.

In another aspect, described herein, is a method to assay for protein-protein interaction comprising: (a) subjecting a cell to a physical or chemical stimulus, said cell comprising: (i) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a ubiquitin polypeptide; (ii) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a ubiquitin polypeptide, and a transcription regulating polypeptide; and (iii) a third nucleic acid comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element; and (b) conducting at least one assay that measures transcription of said reporter element.

In another aspect, described herein, is a method to assay for protein-protein interaction comprising: (a) subjecting a cell to a physical or chemical stimulus, said cell comprising: (i) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a ubiquitin polypeptide; and (ii) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a ubiquitin polypeptide, and a transcription regulating polypeptide, and comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element; and (b) conducting at least one assay that measures transcription of said reporter element.

In another aspect, described herein, is a method to assay for protein-protein interaction comprising: (a) subjecting a cell to a physical or chemical stimulus, said cell comprising: (i) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a ubiquitin polypeptide, and comprising a regulatory element, which is bound by a transcription regulating polypeptide and a reporter element; and (ii) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a ubiquitin polypeptide, and said transcription regulating polypeptide; wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element; and (b) conducting at least one assay that measures transcription of said reporter element.

In another aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide; (b) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a protease polypeptide; and (c) a third nucleic acid comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; wherein said first fragment of a protease polypeptide and said second fragment of a protease polypeptide form an active protease when said bait polypeptide interacts with said prey polypeptide, whereupon said protease cleavage site is cleaved by said active protease, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element.

In another aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide; (b) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a protease polypeptide, and comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; wherein said first fragment of a protease polypeptide and said second fragment of a protease polypeptide form an active protease when said bait polypeptide interacts with said prey polypeptide, whereupon said protease cleavage site is cleaved by said active protease, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element.

In another aspect, described herein, is a system for protein-protein interaction screening comprising: (a) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide, and comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; (b) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a protease polypeptide; wherein said first fragment of a protease polypeptide and said second fragment of a protease polypeptide form an active protease when said bait polypeptide interacts with said prey polypeptide, whereupon said protease cleavage site is cleaved by said active protease, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element.

In another aspect, described herein, is a method to assay for protein-protein interaction comprising: (a) subjecting a cell to a physical or chemical stimulus, said cell comprising: (i) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide; (ii) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a protease polypeptide; and (iii) a third nucleic acid comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; wherein said first fragment of a protease polypeptide and said second fragment of a protease polypeptide form an active protease when said bait polypeptide interacts with said prey polypeptide, whereupon said protease cleavage site is cleaved by said active protease, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element; and (b) conducting at least one assay that measures transcription of said reporter element.

In another aspect, described herein, is a method to assay for protein-protein interaction comprising: (a) subjecting a cell to a physical or chemical stimulus, said cell comprising: (i) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide; (ii) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a protease polypeptide and comprising a regulatory element, which is bound by said transcription regulating polypeptide, and a reporter element; wherein said first fragment of a protease polypeptide and said second fragment of a protease polypeptide form an active protease when said bait polypeptide interacts with said prey polypeptide, whereupon said protease cleavage site is cleaved by said active protease, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element; and (b) conducting at least one assay that measures transcription of said reporter element.

In another aspect, described herein, is a method to assay for protein-protein interaction comprising: (a) subjecting a cell to a physical or chemical stimulus, said cell comprising: (i) a first nucleic acid encoding a bait polypeptide or prey polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide and comprising a regulatory element, which is bound by said transcription regulating polypeptide and a reporter element; (ii) a second nucleic acid encoding a prey polypeptide or a bait polypeptide coupled to a second fragment of a protease polypeptide; wherein said first fragment of a protease polypeptide, and said second fragment of a protease polypeptide form an active protease when said bait polypeptide interacts with said prey polypeptide, whereupon said protease cleavage site is cleaved by said active protease, said transcription regulating polypeptide is released from said bait polypeptide, binds to said regulatory element, and initiates transcription of said reporter element; and (b) conducting at least one assay that measures transcription of said reporter element.

In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments. However, one skilled in the art will understand that the embodiments provided may be practiced without these details. Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. Further, headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed embodiments.

As used herein the term “about” refers to an amount that is near the stated amount by 10%.

The terms “polypeptide” and “protein” are used interchangeably to refer to a polymer of amino acid residues and are not limited to a minimum length. Polypeptides, including the provided polypeptide chains and other peptides, e.g., linkers and binding peptides, may include amino acid residues including natural and/or non-natural amino acid residues. The terms also include post-expression modifications of the polypeptide, for example, glycosylation, sialylation, acetylation, phosphorylation, and the like. In some aspects, the polypeptides may contain modifications with respect to a native or natural sequence, as long as the protein maintains the desired activity. These modifications may be deliberate, as through site-directed mutagenesis, or may be accidental, such as through mutations of hosts which produce the proteins or errors due to PCR amplification.

Percent (%) sequence identity with respect to a reference polypeptide sequence is the percentage of amino acid residues in a candidate sequence that are identical with the amino acid residues in the reference polypeptide sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence identity, and not considering any conservative substitutions as part of the sequence identity. Alignment for purposes of determining percent amino acid sequence identity can be achieved in various ways that are known for instance, using publicly available computer software such as BLAST, BLAST-2, ALIGN or Megalign (DNASTAR) software. Appropriate parameters for aligning sequences are able to be determined, including algorithms needed to achieve maximal alignment over the full length of the sequences being compared. For purposes herein, however, % amino acid sequence identity values are generated using the sequence comparison computer program ALIGN-2. The ALIGN-2 sequence comparison computer program was authored by Genentech, Inc., and the source code has been filed with user documentation in the U.S. Copyright Office, Washington D.C., 20559, where it is registered under U.S. Copyright Registration No. TXU510087. The ALIGN-2 program is publicly available from Genentech, Inc., South San Francisco, Calif., or may be compiled from the source code. The ALIGN-2 program should be compiled for use on a UNIX operating system, including digital UNIX V4.0D. All sequence comparison parameters are set by the ALIGN-2 program and do not vary.

In situations where ALIGN-2 is employed for amino acid sequence comparisons, the % amino acid sequence identity of a given amino acid sequence A to, with, or against a given amino acid sequence B (which can alternatively be phrased as a given amino acid sequence A that has or comprises a certain % amino acid sequence identity to, with, or against a given amino acid sequence B) is calculated as follows: 100 times the fraction X/Y, where X is the number of amino acid residues scored as identical matches by the sequence alignment program ALIGN-2 in that program's alignment of A and B, and where Y is the total number of amino acid residues in B. It will be appreciated that where the length of amino acid sequence A is not equal to the length of amino acid sequence B, the % amino acid sequence identity of A to B will not equal the % amino acid sequence identity of B to A. Unless specifically stated otherwise, all % amino acid sequence identity values used herein are obtained as described in the immediately preceding paragraph using the ALIGN-2 computer program.

The polypeptides of the systems described herein can be encoded by a nucleic acid. A nucleic acid is a type of polynucleotide comprising two or more nucleotide bases. In certain embodiments, the nucleic acid is a component of a vector that can be used to transfer the polypeptide encoding polynucleotide into a cell. As used herein, the term “vector” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a genomic integrated vector, or “integrated vector,” which can become integrated into the chromosomal DNA of the host cell. Another type of vector is an “episomal” vector, e.g., a nucleic acid capable of extra-chromosomal replication. Vectors capable of directing the expression of genes to which they are operatively linked are referred to herein as “expression vectors.” Suitable vectors comprise plasmids, bacterial artificial chromosomes, yeast artificial chromosomes, viral vectors and the like. In the expression vectors regulatory elements such as promoters, enhancers, polyadenylation signals for use in controlling transcription can be derived from mammalian, microbial, viral or insect genes. The ability to replicate in a host, usually conferred by an origin of replication, and a selection gene to facilitate recognition of transformants may additionally be incorporated. Vectors derived from viruses, such as lentiviruses, retroviruses, adenoviruses, adeno-associated viruses, and the like, may be employed. Plasmid vectors can be linearized for integration into a chromosomal location. Vectors can comprise sequences that direct site-specific integration into a defined location or restricted set of sites in the genome (e.g., AttP-AttB recombination). Additionally, vectors can comprise sequences derived from transposable elements for integration.

As used herein the term “transfection” or “transfected” refers to methods that intentionally introduce an exogenous nucleic acid into a cell through a process commonly used in laboratories. Transfection can be affected by, for example, lipofection, calcium phosphate precipitation, viral transduction, or electroporation. Transfection can be either transient or stable.

System Overview

The systems, nucleic acids, and methods described herein are useful to screen for protein-protein interactions. In certain embodiments, protein-protein interactions can be measured before and after an external stimulus such as a physical or chemical stimulus, or compared to control conditions run in parallel. The chemical stimulus can be an agonistic or antagonistic small molecule or biologic molecule. In certain embodiments, the system is useful for screening for pharmaceutical discovery purposes. The system minimally comprises nucleic acid(s) encoding a bait polypeptide, a prey polypeptide, and a reporter element. The bait polypeptide comprises a first fragment of a cleavable molecule or a cleaving molecule (e.g., a protease). The prey polypeptide comprises a second fragment of a cleavable molecule or a cleaving molecule. In certain embodiments, the prey polypeptide is a library of a plurality of prey polypeptides each encoded by a distinct nucleic acid and paired with a distinct reporter, such as for example a unique molecular identifier. Either the prey polypeptide or the bait polypeptide further comprises a transcription regulating polypeptide. When the two fragments come into close proximity a complete functional cleavable molecule or a cleaving molecule is formed and the transcription regulating polypeptide is released either by cleavage of a fully formed protease supplied by the system, or an endogenous protease that acts on a cleavable molecule. Upon cleavage a transcription activating polypeptide is released. The released transcription activating polypeptide then activates transcription of a reporter gene under the control of a promoter able to be bound by the transcription activating polypeptide. In certain embodiments, the reporter gene is unique to a certain prey polypeptide. Additional optional features of the system include a second transcription regulating provided, either conjugated to the same polypeptide as the first transcription regulating polypeptide or provided on the other polypeptide. Additionally, in certain embodiments, the transcription regulating polypeptide is replaced with a transcriptional repressor polypeptide that can bind a repressor element that is 5′ to a constitutively active reporter element, the reporter element comprising a reporter gene and a UMI. This allows for determining a disruption of a protein-protein interaction. The nucleic acids comprising this system may also comprise additional elements that allow for identification and selection of cells that have been transfected with the components of the system described herein.

In certain embodiments, nucleic acids encoding a bait polypeptide, a prey polypeptide, and comprising a reporter element are present on separate nucleic acid molecules, for example separate plasmids or viral vectors. In certain embodiments, the reporter element is present on the same nucleic acid molecule as the bait polypeptide. In certain embodiments, the reporter element is present on the same nucleic acid molecule as the prey polypeptide.

In certain embodiments, described herein is a method of deploying a system comprising nucleic acid(s) encoding a bait polypeptide, a prey polypeptide, and a reporter element for use in drug discovery. In certain embodiments, the method comprises contacting the nucleic acid(s) with a cell or population of cells under conditions sufficient for the nucleic acid(s) to be internalized and expressed by the cell (e.g., transfected); contacting the cell with a physical or chemical stimulus; and determining activation of the reporter element by one or more assays. In certain embodiments, the method comprises contacting a cell or population of cells comprising nucleic acid(s) encoding a bait polypeptide, a prey polypeptide, and a reporter element; and determining activation of the reporter element by one or more assays.

The system described herein has many uses. One use as a screening tool is depicted in FIGS. 1A and 1B, which depicts a single interaction in a single cell. It will be understood however that this reaction occurs many times in a single cell, and that different cells can comprise different specific prey polypeptides that are part of a library comprising at least 10¹, 10², 10³, 10⁴, 10⁵ distinct prey polypeptides. In a certain non-limiting embodiment, referring to FIG. 1A, a prey polypeptide is coupled to a fragment of either a protease (TEV, left side), or ubiquitin (Ub, right side). The prey polypeptide, which is a library of potential interactors, comprises a complementary fragment of TEV or Ub that can functionally complement the activity of the fragment coupled to the bait. The schematic shows a transmembrane bait, but this could, in certain embodiments, be a soluble cytosolic polypeptide, or one that exists associated with the membrane of an intracellular organelle. Upon interaction of the bait and prey polypeptides, as shown in FIG. 1B, the functionally reconstituted protease (TEV, left) cleaves a protease cleavage site (TCS) to release a transcription factor (TF) that can bind a promoter that activates a reporter element through its activation domain (Gal4). In the case of ubiquitin an endogenous deubiquitinating enzyme (DUB) can cleave the fully reconstituted ubiquitin to release a transcription factor (TF) that can bind a promoter that activates a reporter element through its activation domain (Gal4).

Bait and Prey Polypeptides

The systems, nucleic acids, and methods described herein are useful in interrogating protein-protein interactions between a bait polypeptide and a prey polypeptide. The interaction of bait or prey polypeptides may be of interest if they play a role in the pathology or etiology of a human disease. Therefore, systems that can provide multiplexed and efficient methods of testing interactions between a bait polypeptide and a prey polypeptide that interacts with the bait polypeptide have high utility. In certain embodiments, the bait or prey polypeptide comprises a cell surface expressed receptor or channel protein. Cell surface signaling polypeptides are proteins that are inserted or tethered to the membrane and transduce a signal that effects biological function of the cell when bound by a ligand or effected by a physical stimulus. In certain embodiments, the bait polypeptide comprises a G protein-coupled receptor, a receptor tyrosine kinase, or an ion channel.

In certain embodiments, the bait or prey polypeptide comprises a G protein coupled receptor family member. G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, are ligand binding cell surface signaling proteins. When a ligand binds to the GPCR it causes a conformational change in the GPCR, which allows it to act as a guanine nucleotide exchange factor (GEF). The GPCR can then activate an associated G protein by exchanging the GDP bound to the G protein for a GTP. The G protein's α subunit, together with the bound GTP, can then dissociate from the β and γ subunits to further affect intracellular signaling proteins or target functional proteins directly depending on the α subunit type (Gαs, Gαi/o, Gαq/11, Gα12/13). There are at least about 800 GPCRs encoded in the human genome, broadly divided into Classes A, B, and C.

In certain embodiments, the bait or prey polypeptide comprises a receptor tyrosine kinase family member. Receptor tyrosine kinases (RTKs) are high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Receptor tyrosine kinases have been shown not only to be key regulators of normal cellular processes but also to have a critical role in the development and progression of many types of cancer. There are many classes of RTKs any member of which can be utilized as the bait or prey polypeptide in the systems described herein. In certain embodiments, the RTK bait polypeptide comprises an RTK class I (EGF receptor family) (ErbB family); RTK class II (Insulin receptor family); RTK class III (PDGF receptor family); RTK class IV (VEGF receptors family); RTK class V (FGF receptor family); RTK class VI (CCK receptor family); RTK class VII (NGF receptor family); RTK class VIII (HGF receptor family); RTK class IX (Eph receptor family); RTK class X (AXL receptor family); RTK class XI (TIE receptor family); RTK class XII (RYK receptor family); RTK class XIII (DDR receptor family); RTK class XIV (RET receptor family); RTK class XV (ROS receptor family); RTK class XVI (LTK receptor family); RTK class XVII (ROR receptor family); RTK class XVIII (MuSK receptor family); RTK class XIX (LMR receptor); or RTK class XX (Undetermined) member.

In certain embodiments, the bait or prey polypeptide comprises an ion channel. Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Ion channels may be classified by gating such as voltage gating, ligand gating, cyclic nucleotide gating, mechanosensitive gating, gating by other ions (e.g., calcium), light gating, or temperature gating. Ion channels may also be classified by type of ion gated and include potassium, sodium, calcium, protons, non-selective cation, or chloride.

In certain embodiments, the bait or prey polypeptide comprises an intracellular signaling protein. In certain embodiments, the intracellular signaling protein comprises a nuclear hormone receptor. Nuclear hormone receptors are a class of intracellular proteins which are bound by small-molecule ligands and interact with other proteins to initiate transcription in the nucleus. Nuclear hormone receptors can exist in the cytosol associated with chaperone molecules or in the nucleus associated with DNA. Nuclear hormone receptors are divided into several groups as follows: Thyroid hormone receptor; Retinoic acid receptor; Peroxisome proliferator-activated receptor; Rev-ErbA; RAR-related orphan receptor; Liver X receptor-like; Vitamin D receptor-like; NRs with two DNA binding domains; Hepatocyte nuclear factor-4; Retinoid X receptor; Testicular receptor; TLX/PNR; COUP/EAR; Estrogen receptor; Estrogen related receptor; 3-Ketosteroid receptors; NGFIB/NURR1/NOR1; SF1/LRH1; GCNF; and DAX/SHP. Within these groups Nuclear hormone receptors are denoted by an NRNC Symbol: NR1A1; NR1A2; NR1B1; NR1B2; NR1B3; NR1C1; NR1C2; NR1C3; NR1D1; NR1D2; NR1F1; NR1F2; NR1F3; NR1H3; NR1H2; NR1H4; NR1H5[44]; NR1I1; NR1I2; NR1I3; NR1X1; NR1X2; NR1X3; NR2A1; NR2A2; NR2B1; NR2B2; NR2B3; NR2C1; NR2C2; NR2E1; NR2E3; NR2F1; NR2F2; NR2F6; NR3A1; NR3A2; NR3B1; NR3B2; NR3B3; NR3C1; NR3C2; NR3C3; NR3C4; NR4A1; NR4A2; NR4A3; NR5A1; NR5A2; NR6A1; NR0B1; or NR0B2. In certain embodiments, the bait or prey polypeptide comprises any one or more of: NR1A1; NR1A2; NR1B1; NR1B2; NR1B3; NR1C1; NR1C2; NR1C3; NR1D1; NR1D2; NR1F1; NR1F2; NR1F3; NR1H3; NR1H2; NR1H4; NR1H5[44]; NR1I1; NR1I2; NR1I3; NR1X1; NR1X2; NR1X3; NR2A1; NR2A2; NR2B1; NR2B2; NR2B3; NR2C1; NR2C2; NR2E1; NR2E3; NR2F1; NR2F2; NR2F6; NR3A1; NR3A2; NR3B1; NR3B2; NR3B3; NR3C1; NR3C2; NR3C3; NR3C4; NR4A1; NR4A2; NR4A3; NR5A1; NR5A2; NR6A1; NR0B1; or NR0B2.

Generally, the methods used herein will be used to interrogate one or a small number of bait polypeptides compared to a large number of prey polypeptides. For example, in GPCR signaling, multiple GPCRs might interact with a single Gα subunit. A common Gα (the bait polypeptide) may be tested with a large amount of GPCRs (prey polypeptide). In certain embodiments, the prey polypeptide is supplied as a plurality of prey polypeptides, encoded by a plurality of nucleic acids, that interact or potentially interact with a single bait polypeptide.

Assay Methods

The system described above can be effectively utilized using a variety of methods. The system is useful in methods to interrogate protein-protein interactions, both at a steady-state and in response to a physical or chemical stimulus. When the reporter element comprises a UMI mated to a particular prey polypeptide the system can be deployed in a multiplexed assay.

In one non-limiting, illustrative example, a plurality of cells are incubated in one well of a multi-well plate. The plurality of cells are transfected with a plurality of nucleic acids encoding a library of prey polypeptides coupled to a transcription regulating polypeptide and comprising reporter elements with a prey polypeptide specific UMI. The cells can already comprise a nucleic acid encoding a bait polypeptide, or the nucleic acid encoding the bait polypeptide can be transfected along with the prey polypeptide. The transfected cells are then contacted with a chemical stimulus, after a sufficient amount of time to allow for expression of a reporter gene comprising the UMI, cell lysates are harvested, mRNA is reverse transcribed, and sequencing of the UMIs is performed by a next-generation sequencing technology. Sequencing results will indicate if transcription was activated, and the magnitude of any activation. In this example, activation would be indicative of a chemical stimulus causing the prey polypeptide to closely associate with the bait polypeptide. If the prey polypeptide comprises a transcriptional repressor then the opposite interaction can be interrogated (e.g., a chemical stimulus leading to disruption of a protein-protein interaction).

In certain embodiments, the assays are carried out in multiwell formats such as 6, 12, 24, 48, 96, or 384-well format. In certain embodiments, each well is supplied with a different test chemical, or the test chemicals are supplied in duplicate, triplicate, or quadruplicate wells. The assay can also comprise one or more positive or a negative control wells.

Split-Molecules

In certain embodiments, the systems, nucleic acids, and methods described herein rely on molecular complementation of two fragments of a cleavable molecule. For example, the bait polypeptide comprises a first fragment and the prey polypeptide comprises a second fragment. While the first and second fragment can overlap each fragment independently lacks full function. As a result, when the bait polypeptide and the prey polypeptide are brought into proximity the first and second fragment combine to form a single cleavable molecule.

In certain embodiments, the cleavable molecule for use with the systems, nucleic acids, and methods described herein is a ubiquitin molecule. Ubiquitin is a 76 amino acid protein that is highly conserved amongst eukaryotes and plays a key role in protein homeostasis. When ubiquitin is added to a polypeptide it marks that polypeptide for destruction by various cellular processes. Ubiquitin is recycled by cleavage from the marked polypeptide by a deubiquitinating enzyme. The Ubiquitin-60S ribosomal protein L40 comprises the following sequence: MQIFVKTLTGKTITLEVEPSDTIENVKAKIQDKEGIPPDQQRLIFA GKQLEDGRTLSDYNIQKESTLHLVLRLRGG (SEQ ID NO: 1). In certain embodiments, the nucleic acids described herein encode a fragment of a ubiquitin molecule at least about 25, 30, 35, 40, 45, or 50 amino acids in length, or any integer therein, and at least about 90%, 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 1. In certain embodiments, a first fragment of a ubiquitin polypeptide is a C-terminal fragment of a ubiquitin polypeptide (Cub), and a second fragment of a ubiquitin polypeptide is an N-terminal fragment of a ubiquitin polypeptide (Nub). In certain embodiments, a first fragment of a ubiquitin polypeptide is an N-terminal fragment of a ubiquitin polypeptide (Nub), and a second fragment of a ubiquitin polypeptide is a C-terminal fragment of a ubiquitin polypeptide (Cub).

In certain embodiments, the systems, nucleic acids, and methods described herein rely on molecular complementation of two fragments of a protease molecule. For example, the bait polypeptide comprises a first fragment and the prey polypeptide comprises a second fragment. While the first and second fragment can overlap each fragment independently lacks full function. As a result, when the bait polypeptide and the prey polypeptide are brought into proximity the first and second fragment combine to form a single functional protease molecule.

In certain embodiments, the functional protease for use with the methods, nucleic acids, and systems described herein is a from Tobacco Etch Virus nuclear-inclusion-a endopeptidase (TEV protease). TEV is a member of the PA clan of chymotrypsin-like proteases. The amino acid sequence of TEV is set forth in SLFKGPRDYNPIS STICHLTNESDGHTTSLYGIGFGPFIITNKHLFRRNNGTLLVQSLHGVF KVKNTTTLQQHLIDGRDMIIIRMPKDFPPFPQKLKFREPQREERICLVTTNFQTKSMSSMV SDTSCTFPSSDGIFWKHWIQTKDGQCGSPLVSTRDGFIVGIHSASNFTNTNNYFTSVPKNF MELLTNQEAQQWVSGWRLNADSVLWGGHKVFMVKPEEPFQPVKEATQLMN SEQ ID NO: 2. In certain embodiments, the nucleic acids described herein encode a fragment of a TEV at least about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 amino acids in length, or any integer therein, and at least about 90%, 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: X. TEV is highly specific and cleaves a polypeptide comprising the amino acid sequence EXLYΦQ\φ where X is any residue, Φ is any large or medium hydrophobic residue and φ is any small hydrophobic or polar residue. TEV exhibits optimal efficiency against the ENLYFQ\S amino acid sequence. In certain embodiments, a first fragment of a TEV polypeptide is a C-terminal fragment of a TEV polypeptide (CTEV), and a second fragment of a TEV polypeptide is an N-terminal fragment of a TEV polypeptide (NTEV). In certain embodiments, a first fragment of a TEV polypeptide is an N-terminal fragment of a TEV polypeptide (NTEV), and a second fragment of a TEV polypeptide is a C-terminal fragment of a ubiquitin polypeptide (CTEV).

Transcription Factors

In the methods, nucleic acids, and systems described herein a transcription regulating polypeptide is further present coupled to the bait polypeptide or the prey polypeptide. Upon molecular complementation of a split cleavage molecule or a split cleavable molecule the transcription regulating polypeptide is cleaved and released in an active form. This cleavage can be affected by either an endogenous enzyme (e.g., a deubiquitinating enzyme), or by the action of the split molecule itself (e.g., a reconstituted TEV protease). In certain embodiments, a transcription regulating polypeptide is coupled to the prey polypeptide. In certain embodiments, a transcription regulating polypeptide is coupled to the bait polypeptide. In certain embodiments, the system comprises two transcription regulating polypeptides that are coupled to the same polypeptide or different polypeptides. In certain embodiments, the prey polypeptide is coupled to a transcription regulating polypeptide; and the bait polypeptide is coupled to a transcription regulating polypeptide.

In certain embodiments, the transcription regulating polypeptide is a transcription factor. The system described herein is compatible with any transcription factor commonly or potentially useable in a reporter assay. Common transcription factors used include LexA, Gal4, VP16 (from Herpes Simplex Virus), heat shock factor (HSF), NFAT, or CREB. In certain embodiments, the transcription factor is a synthetic transcription factor comprising a DNA bonding domain from a first transcription factor, and a transcription regulating domain from a second transcription factor. In certain embodiments, the transcription factor comprises a GAL4-VP16 chimeric transcription factor. In certain embodiments, the transcription factor comprises a GAL4-VPR chimeric transcription factor. The sequence of the Gal4-VPR chimeric transcription factor is given by the sequence set forth in MKLLSSIEQACDICRLKKLKCSKEKPKCAKCLKNNWECRYSPKTKRSPLTRAHLTEVE SRLERLEQLFLLIFPREDLDMILKMDSLQDIKALLTGLFVQDNVNKDAVTDRLASVETD MPLTLRQHRISATSSSEESSNKGQRQLTVSASGSGRAGKPIPNPLLGLDSTDALDDFDLD MLGSDALDDFDLDMLGSDALDDFDLDMLGSDALDDFDLDMLGSPKKKRKVGSQYLPD TDDRHRIEEKRKRTYETFKSIMKKSPFSGPTDPRPPPRRIAVPSRSSASVPKPAPQPYPFTS SLSTINYDEFPTMVFPSGQISQASALAPAPPQVLPQAPAPAPAPAMVSALAQAPAPVPVL APGPPQAVAPPAPKPTQAGEGTLSEALLQLQFDDEDLGALLGNSTDPAVFTDLASVDNS EFQQLLNQGIPVAPHTTEPMLMEYPEAITRLVTGAQRPPDPAPAPLGAPGLPNGLLSGDE DFSSIADMDFSALLSQISSGSGSGSRDSREGMFLPKPEAGSAISDVFEGREVCQPKRIRPFH PPGSPWANRPLPASLAPTPTGPVHEPVGSLTPAPVPQPLDPAPAVTPEASHLLEDPDEETS QAVKALREMADTVIPQKEEAAICGQMDLSHPPPRGHLDELTTTLESMTEDLNLDSPLTPE LNEILDTFLNDECLLHAMHISTGLSIFDTSLF, SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence at least about 90%, 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 10.

In certain embodiments, the system can provide information on a loss of protein-protein interaction, by employing a transcriptional repressor. In certain embodiments, the transcription regulating polypeptide is a transcriptional repressor. In certain embodiments, the transcriptional repressor comprises a KRAB domain (sequence RTLVTFKDVFVDFTR EEWKLLDTAQQIVYRNVMLENYKNLVSLGYQLTKPDVILRLEKGEEP) SEQ ID NO: 4. In certain embodiments, the transcriptional repressor is a synthetic repressor comprising a DNA bonding domain from a first transcription factor, and a transcriptional repressor domain from a transcriptional repressor protein. In certain embodiments, the transcriptional repressor with an amino acid sequence at least about 90%, 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 4.

In an aspect the transcription regulating polypeptide is a synthetic transcription factor Synthetic transcription factors are artificial proteins capable of targeting and modulating gene expression. Some synthetic transcription factors are chimeric proteins containing domains from multiple different genes. In certain embodiments, synthetic transcription factors comprise a DNA binding domain from one gene and transcriptional regulatory domain from another gene.

In certain embodiments, said synthetic transcription factor has a higher specificity for a regulatory element nucleotide sequence than any endogenous transcription factor. In certain embodiments, said synthetic transcription factor binds a synthetic transcription factor promoter nucleotide sequence not capable of being bound by an endogenous promoter. In certain embodiments, said synthetic transcription factor results in less background production of a reporter than would occur with use of an endogenous transcription factor.

In certain embodiments, said DNA binding domain is non-endogenous to a cell containing a transcriptional relay system of the present invention. In certain embodiments, said DNA binding domain from a first transcription factor is from Gal4, PPR1, LexA, Lac9, or combinations thereof. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MKLLS SIEQACDICRLKKLKCSKEKPKCAKCLKNNWECRYSPKTKRSPLTRAHLTEVES RLERLEQLFLLIFPREDLDMILKMDSLQDIKALLTGLFVQDNVNKDAVTDRLASVETDM PLTLRQHRISATSSSEESSNKGQRQLTVS, SEQ ID NO: 21. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MKKKNSKKSNRTDSKRGDSNGSKSRTACKRCRKKKCDSCKRCAKVCVSDATGKDVRS YVDRAVMIVIRVKYGVDTKRGNATSDDDKKYSSVSS, SEQ ID NO: 22. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MKSRTACKRCRLKKIKCDQEFPSCKRCAKLEVPCYSPKTKRSPLTRAHLTEVESRLERLE QLFLLIFPREDLDMILKMDSLQDIKALLTGLFVQDNVNKDAVTDRLASVETDMPLTLRQ HRISATSSSEESSNKGQRQLTVS, SEQ ID NO: 23. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MKSRTACKRCRLKKIKCDQEFPSCKRCAKLEVPCVSSPKTKRSPLTRAHLTEVESRLERL EQLFLLIFPREDLDMILKMDSLQDIKALLTGLFVQDNVNKDAVTDRLASVETDMPLTLR QHRISATSSSEESSNKGQRQLTVS, SEQ ID NO: 24. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MNKKSSEVMHQACDACRKKKWKCSKTVPTCTNCLKYNLDCVYSPQVVRTPLTRAHLT EMENRVAELEQFLKELFPVWDIDRLLQQKDTYRIRELLTMGSTNTVPGLASNNIDSSLEQ PVAFGTAQPAQSLSTDPAVQSQAYPMQPV, SEQ ID NO: 25. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MNKKSSEVMHQACVECRQQKSKCDAHERAPEPCTKCAKKNVPCIVYSPQVVRTPLTRA HLTEMENRVAELEQFLKELFPVWDIDRLLQQKDTYRIRELLTMGSTNTVPGLASNNIDSS LEQPVAFGTAQPAQSLSTDPAVQSQAYPMQPV, SEQ ID NO: 26. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MNKKSSEVMHQACKRCRLKKIKCDQEFPSCKRCLKYNLDCVYSPQVVRTPLTRAHLTE MENRVAELEQFLKELFPVWDIDRLLQQKDTYRIRELLTMGSTNTVPGLASNNIDSSLEQP VAFGTAQPAQSLSTDPAVQSQAYPMQPV, SEQ ID NO: 27. In certain embodiments, said DNA binding domain comprises an amino acid sequence set forth in MNKKSSEVMHQACKRCRLKKIKCDQEFPSCKRCAKLEVPCVYSPQVVRTPLTRAHLTE MENRVAELEQFLKELFPVWDIDRLLQQKDTYRIRELLTMGSTNTVPGLASNNIDSSLEQP VAFGTAQPAQSLSTDPAVQSQAYPMQPV, SEQ ID NO: 28.

In certain embodiments, said DNA binding domain comprises an amino acid sequence variant of SEQ ID NO: 1. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 1 is R15W, K23P, K23T, K23W, K23M, K23N, F68R, F68Q, L69P, L70P, Q9E, Q9A, Q9N, R15K, R15A, R15M, K18R, K18A, K18M, K23R, K23A, K23M, or combinations thereof. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is R15W. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23P. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23T. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23W. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23M. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23N. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is F68R. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is F68Q. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is L69P. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is L70P. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is Q9E. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is Q9A. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is Q9N. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is R15K. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is R15A. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is R15M. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K18R. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K18A. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K18M. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23R. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23A. In certain embodiments, the amino acid sequence variant of SEQ ID NO: 21 is K23M.

In certain embodiments, said transcription activating domain from a second transcription factor is from VP64, p65, and Rta, and combinations thereof. In certain embodiments, said transcription activating domain comprises the amino acid sequence set forth in: RAGKPIPNPLLGLDSTDALDDFDLDMLGSDALDDFDLDMLGSDALDDFDLDMLGSD ALDDFDLDMLGSPKKKRKVGSQYLPDTDDRHRIEEKRKRTYETFKSIMKKSPF SGPTDP RPPPRRIAVPSRSSASVPKPAPQPYPFTSSLSTINYDEFPTMVFPSGQISQASALAPAPPQVL PQAPAPAPAPAMVSALAQAPAPVPVLAPGPPQAVAPPAPKPTQAGEGTLSEALLQLQFD DEDLGALLGNSTDPAVFTDLASVDNSEFQQLLNQGIPVAPHTTEPMLMEYPEAITRLVTG AQRPPDPAPAPLGAPGLPNGLLSGDEDFSSIADMDFSALLSQISSGSGSGSRDSREGMFLP KPEAGSAISDVFEGREVCQPKRIRPFHPPGSPWANRPLPASLAPTPTGPVHEPVGSLTPAP VPQPLDPAPAVTPEASHLLEDPDEETSQAVKALREMADTVIPQKEEAAICGQMDLSHPPP RGHLDELTTTLESMTEDLNLDSPLTPELNEILDTFLNDECLLHAMHISTGLSIFDTSLF, SEQ ID NO: 14.

In certain embodiments, the nucleic acids described herein encode a transcription factor with a VPR amino acid sequence at least 90% 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 14. In certain embodiments, the nucleic acids described herein encode a transcription factor with a VPR amino acid sequence at least 90% identical to that set forth in SEQ ID NO: 14. In certain embodiments, the nucleic acids described herein encode a transcription factor with a VPR amino acid sequence at least 95% identical to that set forth in SEQ ID NO: 14. In certain embodiments, the nucleic acids described herein encode a transcription factor with a VPR amino acid sequence at least 97% identical to that set forth in SEQ ID NO: 14. In certain embodiments, the nucleic acids described herein encode a transcription factor with a VPR amino acid sequence at least 98% identical to that set forth in SEQ ID NO: 14. In certain embodiments, the nucleic acids described herein encode a transcription factor with a VPR amino acid sequence at least 99% identical to that set forth in SEQ ID NO: 14. In certain embodiments, the nucleic acids described herein encode a transcription factor with a VPR amino acid sequence 100% identical to that set forth in SEQ ID NO: 14.

In certain embodiments, a transcription activating domain on a synthetic transcription factor comprises an amino acid sequence variant that increases or decreases transcriptional activation. In certain embodiments, said transcription activating domain comprising an amino acid sequence variant that increases or decreases transcriptional activation is a sequence variant of SEQ ID NO: 14.

In certain embodiments, a synthetic transcription factor encoded by a nucleic acid sequence of a transcription factor nucleic acid comprises a polypeptide sequence that destabilizes said synthetic transcription factors, also termed a “degron.” In certain embodiments, said polypeptide sequence that destabilizes said transcription factor comprises a PEST polypeptide sequence. A PEST polypeptide sequence is a polypeptide sequence containing a plurality of amino acids, wherein said polypeptide sequence is rich in the amino acids proline, glutamic acid, serine, and/or threonine. In certain embodiments, said polypeptide sequence that destabilizes said transcription factor comprises a CL1 polypeptide sequence. A CL1 polypeptide sequence may act as a degradation signal, leading to a shorter half-life of the resulting synthetic transcription factor. In certain embodiments, said polypeptide sequence that destabilizes said synthetic transcription factor aids in reduction of background signal of a reporter.

In certain embodiments, said synthetic transcription factor comprises a GAL4-VP16 chimeric transcription factor. In certain embodiments, the transcription factor comprises a GAL4-VPR chimeric transcription factor. The sequence of the Gal4-VPR chimeric transcription factor is given by the sequence set forth in MKLLSSIEQACDICRLKKLKCSKEKPKCAKCLKNNWECRYSPKTKRSPLTRAHLTEVE SRLERLEQLFLLIFPREDLDMILKMDSLQDIKALLTGLFVQDNVNKDAVTDRLASVETD MPLTLRQHRISATSSSEESSNKGQRQLTVSASGSGRAGKPIPNPLLGLDSTDALDDFDLD MLGSDALDDFDLDMLGSDALDDFDLDMLGSDALDDFDLDMLGSPKKKRKVGSQYLPD TDDRHRIEEKRKRTYETFKSIMKKSPFSGPTDPRPPPRRIAVPSRSSASVPKPAPQPYPFTS SLSTINYDEFPTMVFPSGQISQASALAPAPPQVLPQAPAPAPAPAMVSALAQAPAPVPVL APGPPQAVAPPAPKPTQAGEGTLSEALLQLQFDDEDLGALLGNSTDPAVFTDLASVDNS EFQQLLNQGIPVAPHTTEPMLMEYPEAITRLVTGAQRPPDPAPAPLGAPGLPNGLLSGDE DFSSIADMDFSALLSQISSGSGSGSRDSREGMFLPKPEAGSAISDVFEGREVCQPKRIRPFH PPGSPWANRPLPASLAPTPTGPVHEPVGSLTPAPVPQPLDPAPAVTPEASHLLEDPDEETS QAVKALREMADTVIPQKEEAAICGQMDLSHPPPRGHLDELTTTLESMTEDLNLDSPLTPE LNEILDTFLNDECLLHAMHISTGLSIFDTSLF, SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence at least 90%, 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence at least 90% identical to that set forth in SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence at least 95% identical to that set forth in SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence at least 97% identical to that set forth in SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence at least 98% identical to that set forth in SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence at least 99% identical to that set forth in SEQ ID NO: 10. In certain embodiments, the nucleic acids described herein encode a transcription factor with an amino acid sequence 100% identical to that set forth in SEQ ID NO: 10.

In certain embodiments, said synthetic transcription factor comprises a Gal4 DNA binding domain given by the amino acid sequence set forth in SEQ ID NO: 21. In certain embodiments, said synthetic transcription factor comprises a DNA binding domain with an amino acid sequence at least 90% 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 21. In certain embodiments, said synthetic transcription factor comprises a DNA binding domain with an amino acid sequence at least 90% identical to that set forth in SEQ ID NO: 21. In certain embodiments, said synthetic transcription factor comprises a DNA binding domain with an amino acid sequence at least 95% identical to that set forth in SEQ ID NO: 21. In certain embodiments, said synthetic transcription factor comprises a DNA binding domain with an amino acid sequence at least 97% identical to that set forth in SEQ ID NO: 21. In certain embodiments, said synthetic transcription factor comprises a DNA binding domain with an amino acid sequence at least 98% identical to that set forth in SEQ ID NO: 21. In certain embodiments, said synthetic transcription factor comprises a DNA binding domain with an amino acid sequence at least 99% identical to that set forth in SEQ ID NO: 21. In certain embodiments, said synthetic transcription factor comprises a DNA binding domain with an amino acid sequence 100% identical to that set forth in SEQ ID NO: 21.

In certain embodiments, said synthetic transcription factor comprises a transcription activating domain from VP64 given by the amino acid sequence set forth in RAGKPIPNPLLGLDSTDALDDFDLDMLGSDALDDFDLDMLGSDALDDFDLDMLGSDAL DDFDLDMLGSPKKKRKV, SEQ ID NO: 11. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 90% 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 11. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 90% identical to that set forth in SEQ ID NO: 11. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 95% identical to that set forth in SEQ ID NO: 11. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 97% identical to that set forth in SEQ ID NO: 11. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 98% identical to that set forth in SEQ ID NO: 11. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 99% identical to that set forth in SEQ ID NO: 11. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence 100% identical to that set forth in SEQ ID NO: 11.

In certain embodiments, said synthetic transcription factor comprises a transcription activating domain from p65 given by the amino acid sequence set forth in QYLPDTDDRHRIEEKRKRTYETFKSIMKKSPFSGPTDPRPPPRRIAVPSRSSASVPKPAPQP YPFTSSLSTINYDEFPTMVFPSGQISQASALAPAPPQVLPQAPAPAPAPAMVSALAQAPAP VPVLAPGPPQAVAPPAPKPTQAGEGTLSEALLQLQFDDEDLGALLGNSTDPAVFTDLAS VDNSEFQQLLNQGIPVAPHTTEPMLMEYPEAITRLVTGAQRPPDPAPAPLGAPGLPNGLL SGDEDFSSIADMDFSALLSQISS, SEQ ID NO: 12. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 90% 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 12. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 90% identical to that set forth in SEQ ID NO: 12. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 95% identical to that set forth in SEQ ID NO: 12. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 97% identical to that set forth in SEQ ID NO: 12. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 98% identical to that set forth in SEQ ID NO: 12. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 99% identical to that set forth in SEQ ID NO: 12. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence 100% identical to that set forth in SEQ ID NO: 12.

In certain embodiments, said synthetic transcription factor comprises a transcription activating domain from Rta given by the amino acid sequence set forth in RDSREGMFLPKPEAGSAISDVFEGREVCQPKRIRPFHPPGSPWANRPLPASLAPTPTGPVH EPVGSLTPAPVPQPLDPAPAVTPEASHLLEDPDEETSQAVKALREMADTVIPQKEEAAIC GQMDLSHPPPRGHLDELTTTLESMTEDLNLDSPLTPELNEILDTFLNDECLLHAMHISTG LSIFDTSLF, SEQ ID NO: 13. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 90% 95%, 97%, 98%, 99%, or 100% identical to that set forth in SEQ ID NO: 13. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 90% identical to that set forth in SEQ ID NO: 13. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 95% identical to that set forth in SEQ ID NO: 13. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 97% identical to that set forth in SEQ ID NO: 13. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 98% identical to that set forth in SEQ ID NO: 13. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence at least 99% identical to that set forth in SEQ ID NO: 13. In certain embodiments, said synthetic transcription factor comprises a transcription activating domain with an amino acid sequence 100% identical to that set forth in SEQ ID NO: 13.

Reporter Elements

The reporter element minimally comprises a regulatory element that is able to be bound by the transcription regulating polypeptide and a reporter gene. The reporter gene minimally comprises a unique molecular identifier (UMI). A unique molecular identifier is a nucleotide sequence that is unique to a given prey polypeptide. Activation of the UMI reporter gene by the cleaved transcriptional activator can be determined by sequencing. In certain embodiments, the reporter element comprises a UMI and an additional reporter gene selected from a fluorescent protein, a luciferase gene, a beta-galactosidase gene, a beta-glucuronidase gene, a chloramphenicol acetyltransferase gene, a secreted placental alkaline phosphatase gene. These genes encode reporter polypeptides which can be assayed for a specific enzymatic activity, or in the case of a fluorescent reporter can be assayed for fluorescent emissions. In certain embodiments, the fluorescent protein comprises a green fluorescent protein (GFP), a red fluorescent protein (RFP), a yellow fluorescent protein (YFP), or a cyan fluorescent protein (CFP).

The system described herein can utilize many different regulatory sequences that control activation of the reporter gene through transcription factor binding. The regulatory sequence is one that can be bound by the transcription regulating polypeptide or the transcriptional repressor polypeptide detailed above. Generally, it will be configured so that the regulatory sequence is 5′ to the UMI, the reporter gene, or both. In certain embodiments, the regulatory sequence comprises a Gal4-UAS, which is able to be bound by a Gal4-VPR chimeric transcription factor.

A UMI allows for multiplexing of different prey peptides in the same assay since transcription of the UMI will indicate association of a specific prey polypeptide with the bait. The UMI can be any length that allows for sufficient diversity to allow multiplexed determination of an interaction between a bait polypeptide and at least 100, 500, 1,000, 2,000, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000 prey polypeptides. Generally, the UMI will be between 8 and 20 nucleotides in length, however it may be longer. In certain embodiments, the UMI is 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides in length.

Reporter Activation

Reporter activation can be measured in any suitable way that allows sequence determination of the UMI, with a preference for methods that allow sequence determination in a multiplex fashion. In certain embodiments, a next-generation sequencing technology is used to determine the sequence of the UMI. Next generation sequencing encompasses many kinds of sequencing such as pyrosequencing, sequencing-by-synthesis, single-molecule sequencing, second-generation sequencing, nanopore sequencing, sequencing by ligation, or sequencing by hybridization. Next-generation sequencing platforms are those commercially available from lllumina (RNA-Seq) and Helicos (Digital Gene Expression or “DGE”). Next generation sequencing methods include, but are not limited to those commercialized by: 1) 454/Roche Lifesciences including but not limited to the methods and apparatus described in Margulies et al., Nature (2005) 437:376-380 (2005); and U.S. Pat. Nos. 7,244,559; 7,335,762; 7,211,390; 7,244,567; 7,264,929; 7,323,305; 2) Helicos Biosciences Corporation (Cambridge, Mass.) as described in U.S. application Ser. No. 11/167,046, and U.S. Pat. Nos. 7,501,245; 7,491,498; 7,276,720; and in U.S. Patent Application Publication Nos. US20090061439; US20080087826; US20060286566; US20060024711; US20060024678; US20080213770; and US20080103058; 3) Applied Biosystems (e.g. SOLiD sequencing); 4) Dover Systems (e.g., Polonator G.007 sequencing); 5) Illumina, Inc. as described in U.S. Pat. Nos. 5,750,341; 6,306,597; and 5,969,119; and 6) Pacific Biosciences as described in U.S. Pat. Nos. 7,462,452; 7,476,504; 7,405,281; 7,170,050; 7,462,468; 7,476,503; 7,315,019; 7,302,146; 7,313,308; and US Application Publication Nos. US20090029385; US20090068655; US20090024331; and US20080206764. Such methods and apparatuses are provided here by way of example and are not intended to be limiting.

Activation of an additional reporter molecule can be determined using standard assays to detect a luciferase protein, a beta-galactosidase protein, a beta-glucuronidase protein, a chloramphenicol acetyltransferase protein, a secreted placental alkaline phosphatase protein, or a fluorescent protein. Generally, these are enzymatic assays where a detectable signal is produced based upon the proteins enzymatic activity towards a substrate. For example, luciferase expression can be measured in the presence of a luciferase substrate by a luminometer. A fluorescent reporter does not require a substrate, and the signal can be measured by fluorescence microscopy or a fluorescent plate reader. Fluorescent reporters are particularly useful for measuring reporter activation in live cells.

Markers

In certain embodiments, the nucleic acids described herein additionally comprise one or more additional genes that encode a selecting polypeptide or a marking polypeptide. In certain embodiments, the nucleic acids described herein additionally comprise one or more additional genes that encode a polypeptide that confers antibiotic resistance to a transfected cell. For example, the nucleic acids can comprise a selectable marker such as an antibiotic resistance gene that confers antibiotic resistance to neomycin/G418 resistance, puromycin resistance, zeocin resistance, or blasticidin resistance. In certain embodiments, the nucleic acids described herein additionally comprise one or more additional genes that encode a polypeptide that comprises an epitope tag that is expressed on the cell surface. This allows for affinity purification or cell sorting to collect cells that have been transfected with the nucleic acids described. In certain embodiments, the epitope tag comprises a c-Myc tag, a Hemagglutinin (HA) tag, a histidine tag, a V5 tag, or a FLAG tag. In certain embodiments, the nucleic acids described herein additionally comprise one or more additional promotorless genes that encode a fluorescent polypeptide. Such genes are useful when transfection is intended to lead to integration and is targeted for a specific location or landing pad. In these instances, the “landing pad” in the cells genome comprises a promoter that can complement the lack of promotor in the pomotorless gene, and lead to expression of the promotorless gene only when the promoterless gene is integrated into the intended genomic location. Cells with correct integration can be selected by flow cytometry and cell sorting. This type of marker can also ensure that only a single copy of an intended nucleic acid is integrated in the genome and help avoid ectopic overexpression. In certain embodiments, a nucleic acid encoding a bait polypeptide comprises: a gene that encodes a polypeptide that confers antibiotic resistance to a transfected cell; a gene that encodes a polypeptide that comprises an epitope tag that is expressed on the cell surface; or a promotorless gene that encodes a fluorescent polypeptide.

Cells

Cells useful in the method described herein are generally those that are able to be easily rendered transgenic with one or more exogenous nucleic acids encoding the bait polypeptide, the prey polypeptide, or that comprise a reporter element. The system nucleic acid(s) encoding a bait polypeptide, a prey polypeptide, and comprising a reporter element can be transfected or transduced into suitable cell line using methods known in the art, such as calcium phosphate transfection, lipid based transfection (e.g., Lipofectamine™, Lipofectamine-2000™, Lipofectamine-3000™, or Fugene® HD), electroporation, or viral transduction. The cell can also be a population of cells of the same type grown to confluency or near confluency in an appropriate tissue culture vessel.

In certain embodiments, the cell used comprises a stable integration of either the nucleic acid encoding a bait polypeptide, the nucleic acid comprising the reporter element, or both. Stable cell lines can be made using random integration of a linearized nucleic acid, virally or transposon directed integration, or directed integration, for example using site specific recombination between an AttP and an AttB site. In certain embodiments, the cell comprises a single genomic integration of the nucleic acid encoding the bait polypeptide. In certain embodiments, the cell comprises a single genomic integration of the nucleic acid comprising the reporter element. In certain embodiments, the cell comprises a single integration of the nucleic acid encoding the bait polypeptide, and a single genomic integration of the nucleic acid comprising the reporter element.

In certain embodiments, the cell or cell population used in the system is a eukaryotic cell. In certain embodiments, the cell or cell population is a mammalian cell. In certain embodiments, the cell or cell population is a human cell. In certain embodiments, the cell or cell population is SH-SY5Y, Human neuroblastoma; Hep G2, Human Caucasian hepatocyte carcinoma; 293 (also known as HEK 293), Human Embryo Kidney; RAW 264.7, Mouse monocyte macrophage; HeLa, Human cervix epitheloid carcinoma; MRC-5 (PD 19), Human fetal lung; A2780, Human ovarian carcinoma; CACO-2, Human Caucasian colon adenocarcinoma; THP 1, Human monocytic leukemia; A549, Human Caucasian lung carcinoma; MRC-5 (PD 30), Human fetal lung; MCF7, Human Caucasian breast adenocarcinoma; SNL 76/7, Mouse SIM strain embryonic fibroblast; C2C12, Mouse C3H muscle myoblast; Jurkat E6.1, Human leukemic T cell lymphoblast; U937, Human Caucasian histiocytic lymphoma; L929, Mouse C3H/An connective tissue; 3T3 L1, Mouse Embryo; HL60, Human Caucasian promyelocytic leukaemia; PC-12, Rat adrenal phaeochromocytoma; HT29, Human Caucasian colon adenocarcinoma; OE33, Human Caucasian oesophageal carcinoma; OE19, Human Caucasian oesophageal carcinoma; NIH 3T3, Mouse Swiss NIH embryo; MDA-MB-231, Human Caucasian breast adenocarcinoma; K562, Human Caucasian chronic myelogenous leukemia; U-87 MG, Human glioblastoma astrocytoma; MRC-5 (PD 25), Human fetal lung; A2780cis, Human ovarian carcinoma; B9, Mouse B cell hybridoma; CHO-K1, Hamster Chinese ovary; MDCK, Canine Cocker Spaniel kidney; 1321N1, Human brain astrocytoma; A431, Human squamous carcinoma; ATDC5, Mouse 129 teratocarcinoma AT805 derived; RCC4 PLUS VECTOR ALONE, Renal cell carcinoma cell line RCC4 stably transfected with an empty expression vector, pcDNA3, conferring neomycin resistance; HUVEC (S200-05n), Human Pre-screened Umbilical Vein Endothelial Cells (HUVEC); neonatal; Vero, Monkey African Green kidney; RCC4 PLUS VHL, Renal cell carcinoma cell line RCC4 stably transfected with pcDNA3-VHL; Fao, Rat hepatoma; J774A.1, Mouse BALB/c monocyte macrophage; MC3T3-E1, Mouse C57BL/6 calvaria; J774.2, Mouse BALB/c monocyte macrophage; PNT1A, Human post pubertal prostate normal, immortalised with SV40; U-2 OS, Human Osteosarcoma; HCT 116, Human colon carcinoma; MA104, Monkey African Green kidney; BEAS-2B, Human bronchial epithelium, normal; NB2-11, Rat lymphoma; BHK 21 (clone 13), Hamster Syrian kidney; NS0, Mouse myeloma; Neuro 2a, Mouse Albino neuroblastoma; SP2/0-Ag14, Mouse×Mouse myeloma, non-producing; T47D, Human breast tumor; 1301, Human T-cell leukemia; MDCK-II, Canine Cocker Spaniel Kidney; PNT2, Human prostate normal, immortalized with SV40; PC-3, Human Caucasian prostate adenocarcinoma; TF1, Human erythroleukaemia; COS-7, Monkey African green kidney, SV40 transformed; MDCK, Canine Cocker Spaniel kidney; HUVEC (200-05n), Human Umbilical Vein Endothelial Cells (HUVEC); neonatal; NCI-H322, Human Caucasian bronchioalveolar carcinoma; SK.N.SH, Human Caucasian neuroblastoma; LNCaP.FGC, Human Caucasian prostate carcinoma; OE21, Human Caucasian oesophageal squamous cell carcinoma; PSN1, Human pancreatic adenocarcinoma; ISHIKAWA, Human Asian endometrial adenocarcinoma; MFE-280, Human Caucasian endometrial adenocarcinoma; MG-63, Human osteosarcoma; RK 13, Rabbit kidney, BVDV negative; EoL-1 cell, Human eosinophilic leukemia; VCaP, Human Prostate Cancer Metastasis; tsA201, Human embryonal kidney, SV40 transformed; CHO, Hamster Chinese ovary; HT 1080, Human fibrosarcoma; PANC-1, Human Caucasian pancreas; Saos-2, Human primary osteogenic sarcoma; Fibroblast Growth Medium (116K-500), Fibroblast Growth Medium Kit; ND7/23, Mouse neuroblastoma×Rat neuron hybrid; SK-OV-3, Human Caucasian ovary adenocarcinoma; COV434, Human ovarian granulosa tumor; Hep 3B, Human hepatocyte carcinoma; Vero (WHO), Monkey African Green kidney; Nthy-ori 3-1, Human thyroid follicular epithelial; U373 MG (Uppsala), Human glioblastoma astrocytoma; A375, Human malignant melanoma; AGS, Human Caucasian gastric adenocarcinoma; CAKI 2, Human Caucasian kidney carcinoma; COLO 205, Human Caucasian colon adenocarcinoma; COR-L23, Human Caucasian lung large cell carcinoma; IMR 32, Human Caucasian neuroblastoma; QT 35, Quail Japanese fibrosarcoma; WI 38, Human Caucasian fetal lung; HMVII, Human vaginal malignant melanoma; HT55, Human colon carcinoma; TK6, Human lymphoblast, thymidine kinase heterozygote; SP2/0-AG14 (AC-FREE), Mouse×mouse hybridoma non-secreting, serum-free, animal component (AC) free; AR42J, or Rat exocrine pancreatic tumor, or any combination thereof.

EXAMPLES

The following illustrative examples are representative of embodiments of compositions and methods described herein and are not meant to be limiting in any way.

Example 1

Example Protein Interaction Screen

In this example, a screen using a split-ubiquitin or split-TEV system, as configured in FIGS. 1A and 1B, is used to screen for potential compounds that induce GPCR signaling. On day 1, plate cells in a 96-well assay plate at 30,000 cells/well. Plate the cells in 100 uL DMEM+10% FBS and add 50 uL OPTIMEM with 50-300 ng/mL doxycycline, depending on level of GPCR induction desired, 15 ug/mL cumate (for split-ubiquitin) or 7.5 ug/mL cumate (for dual-split-TEV). The cells in this example comprise a stably integrated nucleic acid encoding the bait protein, and a plurality of nucleic acids encoding a prey protein transiently transfected. On day 2, add a test compound at desired concentration in 50 uL OPTIMEM to each well. After about 24 hours, add lysis buffer for either luciferase activity assay or for RNA extraction. RNA can be extracted using standard methods or kits. RNA can be quantified by standard downstream assays such as RT-qPCR or RNASeq. Luciferase activity can be assayed using the Promega Bright-Glo system and can be read on a standard luminometer such as a Thermo Fisher Luminoskan, while RNAseq can be performed on an Illumina MiSeq after sequencing library preparation. An exemplary induction of luciferase is shown in FIG. 2.

Example 2 Dose Response of Spit-TEV and Split-Ub Systems

In this example a spit-TEV or split-UB system is deployed to determine the agonistic response to a given chemical stimulus, in this case the β1 adrenergic agonist Xamoterol.

In this example, a library of cell lines was constructed in either the split-ubiquitin (FIG. 3A) or split-TEV (FIG. 3B) configuration. This library comprises a library of cells each expressing different GPCR prey proteins each paired to a unique RNA barcode. On day 1, cells were plated in a poly-L-lysine coated 384-well assay plate at 22,000 cells/well in 25 uL DMEM+10% FBS. On day 2, the media was replaced with 25 uL OPTI-MEM with 1000 ng/mL doxycycline and 120 ug/mL cumate. On day 3, the media was replaced with 20 uL OPTI-MEM with the vehicle DMSO or a dose range of concentrations of the test compound xamoterol. After about 24 hours, lysis buffer was added for RNA extraction. The extracted RNAs were reverse transcribed and amplified in a single step with Luna One-Step RT-qPCR mix to prepare sequencing libraries, and levels of RNA barcode are quantified by RNAseq.

While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention.

All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure. 

1. A system for protein-protein interaction screening comprising: a) a first nucleic acid encoding a bait polypeptide coupled to a first fragment of a protease polypeptide, a protease cleavage site, and a transcription regulating polypeptide; b) a second nucleic acid encoding a prey polypeptide coupled to a second fragment of a protease polypeptide; and c) a third nucleic acid comprising a reporter element, wherein said reporter element comprises a regulatory element, a first reporter gene and a second reporter gene, wherein said regulatory element is configured to be bound by said transcription regulating polypeptide, wherein said second reporter gene encodes an RNA sequence that is unique to said prey polypeptide. 2.-30. (canceled)
 31. A system for protein-protein interaction screening comprising: a. a first nucleic acid encoding a bait polypeptide coupled to a first fragment of a ubiquitin polypeptide; b. a second nucleic acid encoding a prey polypeptide coupled to a second fragment of a ubiquitin polypeptide and a transcription regulating polypeptide; and c. a third nucleic acid comprising a reporter element, wherein said reporter element comprises a regulatory element, a first reporter gene and a second reporter gene, wherein said regulatory element is configured to be bound by said transcription regulating polypeptide, wherein said second reporter gene encodes an RNA sequence that is unique to said prey polypeptide.
 32. The system of claim 31, wherein said first fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide form a cleavable ubiquitin molecule when said bait polypeptide interacts with said prey polypeptide, whereupon said cleavable ubiquitin molecule is cleaved by a deubiquitinating enzyme, said transcription regulating polypeptide is released from said bait polypeptide, and initiates transcription of said first reporter gene and said second reporter gene.
 33. The system of claim 31, wherein said first fragment of a ubiquitin polypeptide is a C-terminal fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide is an N-terminal fragment of a ubiquitin polypeptide.
 34. The system of claim 31, wherein said first fragment of a ubiquitin polypeptide is an N-terminal fragment of a ubiquitin polypeptide and said second fragment of a ubiquitin polypeptide is a C-terminal fragment of a ubiquitin polypeptide.
 35. The system of claim 31, wherein said transcription regulating polypeptide comprises a synthetic transcription factor.
 36. The system of claim 35, wherein said synthetic transcription factor comprises a fusion of a Gal4 DNA binding domain and-VPR activation domain.
 37. The system of claim 31, wherein said transcription regulating polypeptide comprises a transcriptional repressor.
 38. The system of claim 31, wherein said bait polypeptide or said prey polypeptide is a membrane bound signaling polypeptide.
 39. (canceled)
 40. The system of claim 38, wherein said membrane-bound signaling polypeptide comprises a G protein-coupled receptor. 41.-43. (canceled)
 44. The system of claim 31, wherein said regulatory element comprises an inducible regulatory element.
 45. The system of claim 44, wherein said inducible regulatory element comprises a Gal4 Upstream activation Sequence (Gal4 UAS).
 46. The system of claim 31, wherein said first reporter gene encodes a fluorescent protein, a luciferase protein, a beta-galactosidase, a beta-glucuronidase, a chloramphenicol acetyltransferase, or a secreted placental alkaline phosphatase.
 47. The system of claim 31, wherein said first reporter gene encodes a fluorescent protein or a luciferase protein.
 48. (canceled)
 49. (canceled)
 50. The system of claim 31, wherein said first nucleic acid comprises a sequence that directs site specific integration into a genome.
 51. (canceled)
 52. The system of claim 31, wherein said second nucleic acid comprises a sequence encoding a selectable surface marker.
 53. (canceled)
 54. A cell comprising said first nucleic acid, said second nucleic acid, or said third nucleic acid of claim
 31. 55. The cell of claim 54, wherein said first nucleic acid, said second nucleic acid, or said third nucleic acid are integrated at an integration site for a transposable element.
 56. (canceled)
 57. The cell of claim 54, wherein said first nucleic acid, said second nucleic acid, or said third nucleic acid are integrated as a single copy at a genomic location.
 58. A method for testing a test substances effect on a protein-protein interaction comprising contacting a cell or a populations of cells according to claim 54 to said test substance.
 59. (canceled) 